Vacuum-type circuit interrupter



April 29, 1969 J. c. SOFIANEK K f 3,441,698

VACUUM-TYPE CIRCUIT INTERRUPTER Filed Oct. 3, 1966 /IZ 5F/.1. 610 M fw#/4 SWE /NvE/vTo/: JOSEPH C. Sor/A NEN,

ATTORNEY United States Patent O 3,441,698 VACUUM-TYPE CIRCUITINTERRUPTER Joseph C. Sofanek, Broomall, Pa., assignor `to GeneralElectric Company, a corporation of New York Filed ct. 3, 1966, Ser. No.583,893 Int. Cl. H01h 33/66, 9/30 U.S. Cl. 200-144 6 Claims Thisinvention relates to a vacuum-type circuit interrupter and, moreparticularly, relates to improved shielding structure for protecting theinsulation of such an interrupter from being impaired by thecondensation thereon of arc-generated metallic vapors.

It is customary to protect the tubular insulating housing of avacuum-type circuit interrupter from such vaporcondensation by providingsome form of shielding, preferably of metal, located between theinsulating housing and the arcing gap of the interrupter. This shieldingis intended to intercept and condense arc-generated vapors before theycan reach the insulating housing, thus preventing the vapors fromcondensing on and coating the insulation with metallic particles. Thepresent invention is especially concerned with vapor-condensingshielding of the general type disclosed and claimed in U.S. Patent2,892,912, Greenwood et a1., assigned to the assignee of the presentinvention. This shielding comprises (l) a main shield of tubular formsurrounding the arcing gap and maintained at a potential intermediatethat of the electrodes of the intermpter and (2) a pair of auxiliaryshields of tubular form respectively surrounding the opposite ends ofthe main shield and electrically connected to the electrodes. Theauxiliary shields act to intercept metal vapors that might otherwisebypass the main shield and also provide a desired distribution of theelectric field at the ends of the interrupter.

When the above-described shielding is employed in interrupters that areused for extreme high currents it has been found that small amounts ofmetal have still reached the insulating envelope despite the shielding.The quantity of such metal is minute, but even this minute quantityseems to detrimentally affect the interrupting ability of theinterrupter.

An object of the present invention is to improve the ability of theshielding to condense metal vapors that tend to bypass the main shield.

Another object is to force any sparkover between the main shield andadjacent structure to occur in a location where there is a reducedchance for coating the insulating envelope with metal particlesgenerated by the spark.

Another object is to condense -a large portion of the arc-generatedvapors projected toward the ends of the main shield in a region that isessentially free of electrical stress.

In carrying out the invention in one form, I provide a mainvapor-condensing metal shield of tubular form surrounding the usualarcing gap of the interrupter. This main shield extends longitudinallyof the tubular insulating casing of the interrupter for substantialdistances on opposite sides of the arcing gap and is maintained at apotential intermediate that of the interrupters electrodes followinginterruption. A first pair of auxiliary metal shields of generallytubular form respectively surround the ends of the main shield and arespaced radially outward therefrom. These auxiliary shields arerespectively connected to the electrodes of the interrupter. Incombination with this shielding, I provide additional auxiliary metalshields of generally tubular form that are respectively surrounded bysaid main shield at its opposite ends. These additional auxiliaryshields are spaced radially inwardly from said main shield and areelectrically connected to said electrodes.

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In a preferred form of the invention, the additional shields are soshaped that higher electrical stresses are present in the regionsbetween these additional auxiliary shields and the main shield than arepresent between said first auxiliary shields and the main shield.

For a better understanding of the invention, reference may be had to thefollowing description taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a side elevational view in section of a vacuumtype interrupterembodying one form of the present invention.

FIG. 2 is a plan view taken along the line 2-2 of FIG. 1.

Referring now to FIG. 1, there is shown a vacuumty-pe circuitinterrupter comprising an envelope 10 evacuated to a pressure of 10-4mm. of mercury or lower. The envelope comprises a tubular casing 11 ofinsulating material and metal end caps 12 and 13 joined to the tubularcasing 11 at its opposite ends by suitable vacuumtight seals 14.

Located within the envelope 10 is a pair of relatively movable contacts17 and 18, shown by the solid lines of FIG. 1 in their disengaged oropen position. The upper contact 17 is a stationary contact suitablyattached to a conductive rod 17a, which at its upper end is united tothe upper end cap 12. The lower contact 18 is a movable contact attachedto a conductive operating rod 18a, which is suitably mounted forvertical movement. Upward movement of the contact 18 from its solid lineposition to its dotted line position engages the contacts and thuscloses the interrupter, whereas return movement in a downward directionseparates the contacts and opens the interrupter. l

The operating rod 18a projects freely through an opening in the lowerend cap 13, and a flexible metallic bellows 20 provides a seal about rod18a to allow for vertical movement of the rod without impairing thevacuum inside envelope 10. As shown in FIG. 1, the bellows is secured insealed relationship at its respective opposite ends to the operating rod18a and the lower end cap 13.

Although the present invention is applicable to interrupters havingvarious types of contacts, I have illustrated it in connection with aninterrupter having contacts of the type disclosed and claimed in mycopending application Ser. No. 583,808, filed Oct. 3, 1966, and assignedto the assignee of the present invention. Accordingly, each of theillustrated contacts 17 and 18 is of a disc-shape and has one majorsurface facing the other contact. Each contact comprises a centrallylocated contact-making button 25 suitably brazed to the remainder of thecontact. Each of these contact-making buttons is provided with acentrally located recess 27 so that contact between the buttons occurs-on an annular contact-making area 30 when then contacts are in theirdotted-line engaged position of FIG. l. These annular contact-makingregions 30 are of such a diameter that current owing through the closedcontacts follows a radially outwardly bowing loop-shaped path L, as isindicated by the dot-dash line of FIG. 1. The magnetic effect of currentflowing through this loopshaped path L tends in a well-known manner tolengthen the loop. As a result, when the contacts are separated to forman arc between the areas 30, the magnetic effect of the current throughthe loop will impel the arc radially outward.

As the terminals of the arc move toward the outer periphery of the discs17 and 18, the arc is subjected to a circumferentially acting magneticforce that rotates the arc about the central axis of the discs. Thiscircumferentially acting magnetic force is produced by a plurality ofslots 32 provided in each of the discs and dividing the discs into aplurality of fingers 33 bounded by adjacent pairs of slots. The slotsextend from the outer periphery I of the discs radially inward by pathsthat extend both circumferentially and radially of the discs, as isshown in FIG. 2. These slots 32 correspond to similarly designated slotsin the U.S. Patent 2,949,520 Schneider and, thus, force the currentiiowing to or from an arc terminal on the slotted portion of the contactto follow a path that has a component extending circumferentially of thedisc in the 'vicinity of the arc. This circumferential component of thecurrent path causes current owing through the loop L to develop a netcircumferentially acting force component which tends to rotate the arcabout the central axis of the disc.

This circumferentially acting force lcomponent is high enough to driveeach terminal of the arc across slots 32, thus producing a continuousrotational movement of the arc on the contact surface. This continuousrotational movement of the arc enables higher currents to beinterrupted, apparently because it reduces contact-erosion by the arc,thus reducing the quantity of metal vapors generated and therebypermitting more complete condensation of the metal vapors at currentzero.

For condensing the metal vapors that are generated by the arc, I providevapor-condensing metal shielding 50, 54, 56 and 58. This shieldingcomprises a tubular main shield 50 surrounding the arcing gap 52 andlocated between the insulating casing 11 and the arcing gap. This mainshield 50 extends longitudinally of casing 11 for substantial distanceson opposite sides of the arcing gap 52. Preferably, the tubular mainshield 50 has an enlarged diameter in the region around the contacts 17and 18, as compared to its diameter near its ends, so as to give addedclearance between the shield and the contacts 17, 18. The main shield 50is suitably supported on the insulating casing 12 and is maintained at avoltage approximately midway that of the contact 17 and 18 when theinterrupter is opened. In the illustrated form of the invention, thismidpotential relationship is provided by relying upon the substantiallyequal capacitances present between the shield and opposite ends of theinterrupter.

Surrounding the main shield 50 at its respective opposite ends areauxiliary shields 54 of the general type shown in the aforesaidGreenwood et al. patent. These auxiliary shields 54 are electricallyconnected to the end caps 12 and 13, respectively, and therefore are atthe same potential as the contacts I17 and 18, respectively. Each ofthese auxiliary shields 54 is of a generally tubular form and surroundsthe end of the |main shield 50` in radially-spaced relationship. Theseauxiliary shields 54 serve to intercept and condense metal vapors thatmight bypass the primary shield 50 at its ends. The auxiliary shields 54also serve to relieve the seals 14 of voltage stresses.

Located radially inwardly of the main shield 50 at its opposite ends areadditional auxiliary shields 56. These additional shields 56 ane also ofa generally tubular form and are electrically connected to end caps 12and 13, respectively. Thus, the upper auxiliary shield 56 is at the samepotential as upper contact 17, and the lower shield at the samepotential as lower contact 18.

Each of the auxiliary shields 56 surrounds a space 60 that has one endopen, i.e., the end facing the contacts, and its other end closed oi byan end wall of the interrupter.` At each end of the interrupter, theauxiliary shields 54 and 56 are both spaced from the main shield.

An additional shield 58 of cup-shaped form is provided about the bellows20 to protect the bellows from the arc-generated products.

When an arc is formed across lthe gap 52 during interruption, most ofthe metallic vapors generated by the arc are projected radially outwardfrom the arcing gap and are condensed on the inner surface of the mainshield 50. In the illustrated interrupter, however, a relatively largequantity of metal vapors is also projected lfrom gap 52 through theslots 32 in directions longitudinal of insulating casing 12. A highpercentage of these longitudinally directed vapors are trapped withinthe spaces surrounded by the two auxiliary shields 56. In the case ofthe upwardly directed vapors, most of these trapped vapors areintercepted and condensed either by the inner surface of the upperauxiliary shield 56 or by the lower surface of end cap 12. This trappingand condensation precludes these vapors from finding a path around theupperl end of main shield 50, thus preventing them from reachinginsulating casing 12. In the case of the downwardly directed vapors, thevapors trapped within lower space 60 are condensed either on the innersurface of. lower auxiliary shield 56, the upper surface of end cap 13,or the outer surface of the shield 58 for the bellows. This condensationprevents these vapors form nding a path around the lower end of mainshield 50.

It is to be noted that each of the spaces 60 is a region of very low,virtually zero, electric stress since it is bounded on substantially allsides, except the open side facing the contacts, by metal parts at thesame potential. Even on the open side of space 60, the rcontactthereadjacent is at the same potential as the auxiliary shield 56,thereby precluding the entry into space -60 of a significant electricfield. This very low electric stress greatly reduces the tendency for asparkover to develop between the surface of the metal condensate on thewalls of space k60 and an `adjacent part `such as main shield 50. Suchsparkovers, even `though they are usually self-extinguishing, seem todetra-ct from the interrupting ability of the interrupter. Without theauxiliary shields 56, there is a significant chance for such a sparkoversince the condensate has a rather rough surface that is conducive tolthe initiation of sparkover.

If a sparkover does occur between the main shield 50 and an adjacentpart, it is most desirable that it be located -within the space boundedby the main shield 50 rather than outside this space. This is the casebecause the sparkover, even though it usually quickly extinguishesitself, generates some metallic vapors which are more likely to reachthe casing 11 if the spark is outside the main shield 50. To encourageany sparkover involving main shield 50 to be located inside the mainshield 50, I shape each of the inner auxiliary ,shields 56 so that themaximum electric stress between the main shield 50 and inner auxiliaryshields 56 is greater than that between main shield 50 and the outerauxiliary shields 54. To this end, I provide each auxiliary shield 56with a ared portion 56a at its free end that forms a regionthereadjacent where the electrical stress is higher than in any regionlocated between .shields 50 and 54. The relatively small diameter of theauxiliary shield 56 compared to that of auxiliary shield 54 alsocontributes to the higher stress adjacent portion 56a Of the innershield 54.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from myinvention in its broader aspects; and I, therefore, intend in theappended claims to A cover all such changes and modifications as fallwithin the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A vacuum-type circuit interrupter comprising:

(a) a highly evacuated envelope comprising a tubular casing primarily ofinsulating material,

(b) a pair of electrodes within .said casing deiining an arcing gaptherebetween across which arcs are established during acircuit-interrupting operation,

(c) a main vapor-condensing metal shield of tubular form surroundingsaid arcing gap and extending longitudinally of said tubular casing forsubstantial distances on opposite sides of said gap,

(d) means for maintaining said main shield at a potential intermediatethat of said electrodes following interruption,

(e) a rst pair of auxiliary metal shields ol' generally tubular formrespectively surrounding the ends of said main shield and space-dradially outward therefrom,

(f) means for respectively electrically connecting said auxiliaryshields to said electrodes,

(g) a pair of additional auxiliary metal shields of generally tubularform respectively surrounded by said main shield at its opposite ends,

(h) said additional auxiliary shields beinglspaced radially inward from.said main shield andbein'g yelectrically connected to said electrodes.

2. A vacuum-type circuit interrupter as defined in claim 1 in which eachof said electrodes has openings therein through which metallicvapors areexpelled from said arcing gap longitudinally vof said tubular casingduring an interrupting operation.

3. The circuit interrupter of claim 1 in which the space bounded by eachof said additional auxiliary shields has one end facing said electrodesthat is open and another end remote from said electrodes that issubstantiallyclosed oli by metallic structure extending thereacross.

4. A vacuum-type circuit interrupter as defined in claim 3 in which eachof said electrodes has openings therein through which .metallic vaporsare expelled from said arcing gap longitudinally of said tubular casingdur ing an interrupting operation.

S. A vacuum-type circuit interrupter as defined in claim 1 in which saidauxiliary shields are so shaped that when said interrupter is open,higher electrical stresses are present in the regions between said mainshield and said additional auxiliary shields than in any region betweensaid main shield and said first pair of auxiliary shields.

6. The vacuum type circuit interrupter of claim 5 in which at least oneof said additional auxiliary shields has a flared portion at its freeend surrounded by said main shield, where the highest electric stress ispresent Vbetween said main shield and said one additional auxiliaryshield.

References Cited UNITED STATES PATENTS 2,892,912 6/1959 Greenwood et al.3,185,800 5/1965 Titus. 3,189,715 v6/1965 Jennings. 3,283,100 1v1/1966Frink. 3,372,258 3/1968 POIteI'.

ROBERT s. MACON, Primary Examiner.

U.S. Cl. X.R. ZOO-168

1. A VACUUM-TYPE CIRCUIT INTERRUPTER COMPRISING: (A) A HIGHLY EVACUATED ENVELOPE COMPRISING A TUBULAR CASING PRIMARILY OF INSULATING MATERIAL, (B) A PAIR OF ELECTRODES WITHIN SAID CASING DEFINING AN ARCING GAP THEREBETWEEN ACROSS WHICH ARCS ARE ESTABLISHED DURING A CIRCUIT-INTERRUPTING OPERATION, (C) A MAIN VAPOR-CONDENSING METAL SHIELD OF TUBULAR FORM SURROUNDING SAID ARCING GAP AND EXTENDING LONGITUDINALLLY OF SAID TUBULAR CASING FOR SUBSTANTIAL DISTANCES ON OPPOSITE SIDES OF SAID GAP, (D) MEANS FOR MAINTAINING SAID MAIN SHIELD AT A POTENTIAL INTERMEDIATE THAT OF SAID ELECTRODES FOLLOWING INTERRUPTION, (E) A FIRST PAIR OF AUXILIARY METAL SHIELDS OF GENERALLY TUBULAR FORM RESPECTIVELY SURROUNDING THE ENDS OF SAID MAIN SHIELD AND SPACED RADIALLY OUTWARD THEREFROM, (F) MEANS FOR RESPECTIVELY ELECTRICALLY CONNECTING SAID AUXILIARY SHIELDS TO SAID ELECTRODES, (G) A PAIR OF ADDITIONAL AUXILIARY METAL SHIELDS OF GENERALLY TUBULAR FORM RESPECTIVELY SURROUNDED BY SAID MAIN SHIELD AT ITS OPPOSITE ENDS, (H) SAID ADDITIONAL AUXILIARY SHIELDS BEING SPACED RADIALLY INWARD FROM SAID MAIN SHIELD AND BEING ELECTRICALLY CONNECTED TO SAID ELECTRODES. 